The present invention relates generally to the field of anti-G suit valves, and more specifically to rapid response valves that quickly inflate an anti-G suit to protect pilots flying modern high performance fighter aircraft.
While flying simulated or actual combat maneuvers, a fighter pilot's body undergoes very high accelerations from the rapid changes in speed and direction. These accelerations are generally expressed in units of g, the acceleration of a mass at the surface of the Earth due to gravity. The accelerations of greatest concern to a pilot are those that occur along the vertical Z-axis of the cockpit when the pilot pulls back hard on the aircraft control stick to accomplish a rapid climb or a fast banked turn. The pilot's oxygen-carrying blood is forced away from its regular path between the heart-lungs and the brain, and pools toward the blood vessels of the lower extremities. At sufficiently high G's, the pilot's field of vision narrows as blood flow to the retinas is reduced, and the pilot will finally lose consciousness from insufficient blood flow to the brain.
Pilots fight the effects of high G's by straining maneuvers, tensing the muscles of their torso and extremities to squeeze shut the blood vessels and force blood flow to continue in the upper part of the body. An anti-G suit helps this process by covering the pilot's legs and torso with air bladders which can be inflated to compress the blood vessels in those regions and force blood flow to continue to the brain. A G-suit cannot remain continuously inflated or blood flow to the lower extremities would dangerously cease during low or no acceleration. Therefore, a valve controls the action of the anti-G suit to fill the air bladders only during periods of high G's.
Standard anti-G suit valves in use today are mechanical spring-mass controlled valves, providing pressurized air to the anti-G suit bladders at pressures proportional to acceleration. These valves, in order to avoid unacceptable suit inflation in rough air, incorporate a deadband of one or two G's before permitting pressurized air into the suit bladders. This deadband effect, along with the general sluggishness of the conventional valves, poses a danger to today's pilots because the standard valves cannot trigger quickly enough, or fill the suit bladders rapidly enough, to deal with the rates of acceleration onset achievable by modern high performance aircraft.
Some experienced pilots deal with this response slowness by manual control of the number of G's encountered during flight maneuvers. The pilot typically pulls the stick to a position known from experience to produce, for instance, six G's, a force that an experienced fighter pilot can tolerate immediately, then eases the stick back to cause further acceleration and higher G's as the G-suit bladders begin to fill. In this gradual onset environment, the pilot can observe his symptoms of loss of peripheral vision, tunneling of vision, greyout, and the onset of blackout in order to judge his physiological state, and to moderate his acceleration exposure accordingly.
However, modern jet fighters, such as an F-16, increasingly incorporate computer controlled flight control, or fly-by-wire, systems. In an F-16, the pilot signals through control stick movement a request for a maximum rate maneuver, the aircraft's computer determines what that rate should be, and institutes it immediately. Exposure to high rate of onset, high sustained acceleration without optimal protection places the pilot in an uniquely hazardous physiological environment leading to abrupt loss of consciousness with no warning symptoms because of the exhaustion of the brain's oxygen reserve.
The prior art includes improvements to the mechanically controlled, or inertial, anti-G valves to provide a faster response time. Inertial valves have been modified to make a high flow ready pressure valve that inflates the air bladders more rapidly. Developments have also been made in electronic servo feedback mechanisms for quicker triggering of the anti-G valve, as disclosed in U.S. Pat. No. 3,780,723 to the present inventor, and U.S. Pat. No. 4,243,024 to Crosbie, et al. These patents provide for measuring the rate of change of acceleration (dG/dt or G') as being an earlier predicter of imminent high G acceleration. The circuits in the two patents add G and G' to create a triggering signal that initiates inflation of the anti-G suit bladders after a threshold level of G, G', or a combined G and G', is exceeded. The circuits include a feedback signal from the anti-G suit of the air pressure in the bladders so that a desired suit pressure for a particular acceleration may be maintained. U.S. Pat. No. 4,336,590 to Jacq, et al. describes a microprocessor controlled anti-G suit valve that includes means for monitoring control stick movement to initiate inflation of the air bladders upon control stick movement that indicates imminent high acceleration.
These electronic anti-G valves are valuable improvements to the art, but they are extremely expensive and have not been implemented in actual aircraft. The high flow ready pressure mechanical valves have been incorporated in modern aircraft, but these valves still have a relatively slow response rate and suffer from failure to trigger quickly enough under high rates of acceleration onset. Attempts to improve the response rate of high flow ready pressure valves have been plagued by oscillations. It is thus seen that there is a need for an anti-G suit valve that successfully combines fast response and inflation with low cost and easy implementation so that it may find actual use in modern fighter aircraft.
It is, therefore, a principal object of the present invention to provide a rapidly responding anti-G suit valve that triggers quickly and inflates rapidly.
Another object of this invention is to provide an anti-G suit valve that is low in cost and easy to implement in existing fighter aircraft.
A feature of this invention is that it can be retrofitted as a modification to existing mechanical anti-G valves.
An advantage of this invention is that in case of failure the normal operation of the mechanical valve is not affected, providing a fail operational mode of operation.
Another advantage of this invention is that early initiation of anti-G suit inflation serves as a warning of imminent high acceleration to an otherwise actively engaged pilot.
These and other objects, features and advantages of the present invention will become apparent as the detailed description of certain representative embodiments proceeds.